U.S. patent application number 13/249851 was filed with the patent office on 2013-04-04 for catheter guidance system.
This patent application is currently assigned to KONICA MINOLTA LABORATORY U.S.A., INC.. The applicant listed for this patent is Evgeny Ter-Ovanesyan. Invention is credited to Evgeny Ter-Ovanesyan.
Application Number | 20130085448 13/249851 |
Document ID | / |
Family ID | 47993280 |
Filed Date | 2013-04-04 |
United States Patent
Application |
20130085448 |
Kind Code |
A1 |
Ter-Ovanesyan; Evgeny |
April 4, 2013 |
CATHETER GUIDANCE SYSTEM
Abstract
A catheter guidance system and method for guiding a catheter
through the bloodstream of the patient's cardiovascular system in a
medical procedure. The catheter has a front tip with a heating
element for slightly heating a media surrounding the front tip in a
blood vessel of the patient's cardiovascular system, and two
temperature measuring elements located adjacent to and in front and
behind the heating element respectively for measuring temperatures
in the media at their respective locations. A guidance device is
coupled to the catheter for converting the heating power and
temperature measurement signals to digital signals, processing the
digital signals, and displaying guidance information indicative of
the location of the front tip of the catheter relative to the blood
vessel wall of the patient's cardiovascular system. The guidance
information may be shown by an intuitive traffic light type
display.
Inventors: |
Ter-Ovanesyan; Evgeny;
(South San Francisco, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ter-Ovanesyan; Evgeny |
South San Francisco |
CA |
US |
|
|
Assignee: |
KONICA MINOLTA LABORATORY U.S.A.,
INC.
San Mateo
CA
|
Family ID: |
47993280 |
Appl. No.: |
13/249851 |
Filed: |
September 30, 2011 |
Current U.S.
Class: |
604/113 |
Current CPC
Class: |
A61B 2017/00084
20130101; A61B 2017/00097 20130101; A61B 34/20 20160201; A61B
2017/00088 20130101; A61B 2017/00092 20130101; A61B 2018/00797
20130101; A61B 2018/00809 20130101; A61B 18/1492 20130101; A61B
2018/00791 20130101; A61B 2018/00803 20130101; A61B 2018/00821
20130101; A61B 2018/00714 20130101; A61B 2018/00898 20130101; A61B
2018/00815 20130101; A61B 2090/065 20160201; A61B 90/06
20160201 |
Class at
Publication: |
604/113 |
International
Class: |
A61F 7/12 20060101
A61F007/12 |
Claims
1. A catheter for use in a bloodstream of a patient's
cardiovascular system, comprising: an elongated body with a front
tip and a rear end; a heating element adjacent to the front tip for
heating a media surrounding the front tip in a blood vessel of the
patient's cardiovascular system; and two temperature measuring
elements disposed adjacent to the heating element, one located
between the front tip and the heating element and the other one
located between the rear end and the heating element, for measuring
temperatures in the media at respective locations of the two
temperature measuring elements.
2. A system comprising the catheter of claim 1.
3. The system of claim 2, further comprising: a guidance device for
guiding the catheter through the bloodstream of a patient's
cardiovascular system in a medical procedure; and a cable
electrically and electronically coupling the catheter and the
guidance device for providing a heating power to the catheter and
transmitting electronic signals of the heating power and the
temperature measurements from the catheter to the guidance device;
wherein the guidance device comprises: a data processor for
processing the electronic signals of the heating power and the
temperature measurements and generating display signals indicative
of the location of the front tip of the catheter relative to the
blood vessel wall of the patient's cardiovascular system; and a
display unit coupled to the guidance device for displaying guidance
information based on the display signals.
4. The system according to claim 3, wherein the display unit is an
integral part of the guidance device.
5. The system according to claim 3, wherein the guidance device
keeps the heating power of the heating element of the catheter
constant and calculates a temperature difference between
temperature measurements in the media at the respective locations
of the two temperature measuring elements of the catheter as an
indication of the location of the front tip of the catheter
relative to the blood vessel wall of the patient's cardiovascular
system.
6. The system according to claim 3, wherein the guidance device
keeps the temperature difference between temperature measurements
in the media at the respective locations of the two temperature
measuring elements of the catheter constant and measures the
heating power of the heating element of the catheter as an
indication of the location of the front tip of the catheter
relative to the blood vessel wall of the patient's cardiovascular
system.
7. The system according to claim 3, wherein the guidance
information displayed on the display unit is a traffic light type
display comprising: a red light indicating that the front tip of
the catheter is pressing through the blood vessel wall of the
patient's cardiovascular system; a yellow light indicating that the
front tip of the catheter is contacting the blood vessel wall of
the patient's cardiovascular system; and a green light indicating
that the front tip of the catheter is in the bloodstream in the
blood vessel of the patient's cardiovascular system.
8. A system comprising: a catheter having a body with a front tip
and a rear end, a heating element disposed adjacent to the front
tip for heating a media surrounding the front tip in a blood vessel
of a patient's cardiovascular system, and two or more temperature
measuring elements adjacent to the heating element for measuring
temperatures located between the front tip and the heating element,
and located between the rear end and the heating element
respectively in the media; a data processor for processing
temperature measurement signals from the two or more temperature
measuring elements and generating display signals indicative of the
location of the front tip of the catheter relative to the blood
vessel wall of the patient's cardiovascular system; and a display
unit for displaying guidance information based on the display
signals.
9. The system of claim 8, wherein the catheter includes two
temperature measuring elements, one located between the front tip
and the heating element and the other one located between the rear
end and the heating element, for measuring temperatures in the
media at respective locations of the two temperature measuring
elements.
10. The system according to claim 8, further comprising a cable
electrically and electronically coupling the catheter and the
guidance device for providing electrical power to the catheter and
transmitting electronic signals of a heating power and the
temperature measurements from the catheter to the guidance
device.
11. The system according to claim 8, wherein the device keeps a
heating power of the heating element of the catheter constant and
calculates a temperature difference between the temperature
measurements in the media at the respective locations of the
temperature measuring elements of the catheter as an indication of
the location of the front tip of the catheter relative to the blood
vessel wall of the patient's cardiovascular system.
12. The system according to claim 8, wherein the device keeps the
temperature difference between temperature measurements in the
media at the respective locations of the temperature measuring
elements of the catheter constant and measures the a heating power
of the heating element of the catheter as an indication of the
location of front tip of the catheter relative to the blood vessel
wall of the patient's cardiovascular system.
13. The system according to claim 8, wherein the guidance
information displayed on the display unit is a traffic light type
display comprising: a red light indicating that the front tip of
the catheter is pressing through the blood vessel wall of the
patient's cardiovascular system; a yellow light indicating that the
front tip of the catheter is contacting the blood vessel wall of
the patient's cardiovascular system; and a green light indicating
that the front tip of the catheter is in the bloodstream in the
blood vessel of the patient's cardiovascular system.
14. A method for guiding a catheter through a bloodstream of a
patient's cardiovascular system, wherein the catheter has a rear
end and a front tip with a heating element for heating a media
surrounding the front tip in a blood vessel of the patient's
cardiovascular system, the method comprising: generating
temperature measurement signals from the catheter representing
measured temperatures in the media at locations of the catheter
adjacent to the heating element, in the front of the heating
element between the front tip and the heating element, and in the
back of the heating element between the rear end and the heating
element respectively; processing the temperature measurement
signals and generating display signals indicative of a location of
the front tip of the catheter relative to a blood vessel wall of
the patient's cardiovascular system; and displaying guidance
information based on the display signals.
15. The method according to claim 14, wherein the temperature
measurement signals represent measured temperatures in the media at
two locations, one location being between the front tip and the
heating element and the other location being between the heating
element and the rear end.
16. The method according to claim 14, further comprising the step
of transmitting electronic signals of the temperature measurements
to a guidance device.
17. The method according to claim 14, further comprising the steps
of: supplying electrical power to the catheter; and controlling a
heating power supplied to the catheter.
18. The method according to claim 14, wherein the processing step
comprises: keeping a heating power of the heating element of the
catheter constant; and calculating a temperature difference between
the temperature measurements in the media at the locations in the
front of the heating element and the back of the heating element
respectively as an indication of the location of the front tip of
the catheter relative to the blood vessel wall of the patient's
cardiovascular system.
19. The method according to claim 14, wherein the processing step
comprises: keeping the temperature difference constant between the
temperature measurements in the media at the front of the heating
element and the back of the heating element; and measuring a
heating power of the heating element of the catheter as an
indication of the location of the front tip of the catheter
relative to the blood vessel wall of the patient's cardiovascular
system.
20. The method according to claim 14, wherein the step of
displaying guidance information further comprises the steps of:
displaying a red light indicating that the front tip of the
catheter is pressing through the blood vessel wall of the patient's
cardiovascular system; displaying a yellow light indicating that
the front tip of the catheter is contacting the blood vessel wall
of the patient's cardiovascular system; and displaying a green
light indicating that the front tip of the catheter is in the
bloodstream in the blood vessel of the patient's cardiovascular
system.
21. The system according to claim 3, wherein the guidance device
further comprise a controller for controlling the data processor
and the heating power supplied to the catheter.
22. The system according to claim 8, further comprising a
controller for controlling the data processor and a heating power
supplied to the catheter.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to catheters and catheter
guidance systems, and more particularly it relates to catheters and
cardiac catheter guidance systems used in the bloodstream of a
patient's cardiovascular system.
[0003] 2. Description of Related Art
[0004] Cardiac catheterization technology is growing rapidly, and
there is an increasing demand for simple and inexpensive cardiac
catheters that are safe and easy to use.
[0005] The use of cardiac catheters has revolutionized the
cardiology field. Several notable techniques have been developed
based on the use of cardiac catheters, such as angiography which
involves direct injection of X-ray contrast agent for better
imaging, angioplasty which involves mechanical widening of an
obstructed blood vessel with a balloon, and radio frequency (RF)
ablation which involves burning a small area of the heart which
cause cardiac arrhythmia.
[0006] However, navigating a cardiac catheter in a patient's
cardiovascular system requires great skills of a highly trained
interventional cardiologist. Any damage to the wall of a blood
vessel should be minimized as the damage area might become a place
where atherosclerotic plaque will start forming. Sometimes the
catheter can perforate the wall of a blood vessel causing a
life-threatening emergency. The risk of perforation is especially
high in complex cases, such as for patients with heavily calcified
blood vessels. A simple, inexpensive guidance system can help the
interventional cardiologist to maneuver the cardiac catheter in the
cardiovascular system while minimizing the risk of perforation to
the wall of a blood vessel.
[0007] The most common catheter guidance technique currently in use
is fluoroscopy (X-ray). The drawback is that X-ray exposure to the
patient may be high during long, complex procedures. Other recently
developed catheter-based imaging systems place magnets or
force-contact sensors on a catheter, or utilize near-infrared
imaging, for tracking the catheter movement in the cardiovascular
system. These systems are rather complicated and quite
expensive.
[0008] There is a need for a safe, simple and inexpensive catheter
guidance system for assisting interventional cardiologist in
navigating a catheter in a cardiovascular system, especially in
complex cases, such as for patients with heavily calcified blood
vessels.
SUMMARY
[0009] The present invention is directed to catheters and a
guidance system for cardiac catheters.
[0010] An object of the present invention is to provide a guidance
system or device for assisting a cardiologist to safely maneuver or
navigate a cardiac catheter in a bloodstream of a patient's
cardiovascular system.
[0011] Another object of the present invention is to provide a
method for generating and displaying intuitive guidance information
for assisting a cardiologist to safely maneuver or navigate a
cardiac catheter in a bloodstream of a patient's cardiovascular
system.
[0012] A further object of the present invention is to provide a
cardiac catheter guidance system or device that is simple in design
and construction, inexpensive to produce and easy to use in medical
procedures.
[0013] To achieve these and/or other objects, as embodied and
broadly described, the present invention provides a catheter
guidance system, comprising a catheter for use in the bloodstream
of a patient's cardiovascular system. The catheter comprises an
elongated body with a front tip and a rear end; a heating element
adjacent to the front tip for heating a media surrounding the front
tip in a blood vessel of the patient's cardiovascular system; and
at least two temperature measuring elements disposed adjacent to
the heating element, one located in the front of the heating
element between the front tip and the heating element and the other
one located in the back of the heating element between the rear end
and the heating element, for measuring temperatures in the media at
respective locations of the two temperature measuring elements.
[0014] In one embodiment, the catheter guidance system also
comprises a guidance device for guiding the catheter through the
bloodstream of a patient's cardiovascular system in a medical
procedure; and a cable electrically and electronically coupling the
catheter and the guidance device for providing a heating power to
the catheter and transmitting electronic signals of the heating
power and the temperature measurements from the catheter to the
guidance device.
[0015] According to embodiments of the present invention, the
guidance device may comprise (a) a data processor for processing
the electronic signals of the heating power and the temperature
measurements and generating display signals indicative of the
location of the front tip of the catheter relative to the blood
vessel wall of the patient's cardiovascular system; (a) a
controller for controlling the data processor and the heating power
supplied to the catheter; and (c) a display unit coupled to the
guidance device for displaying guidance information based on the
display signals.
[0016] In another embodiment of the present invention, the guidance
device may comprise (a) an analog/digital (A/D) converter for
converting the heating power and temperature measurement signals to
digital signals; (b) a data processor for processing the digital
signals and generating display signals indicative of the location
of the front tip of the catheter relative to the blood vessel wall
of the patient's cardiovascular system; (c) a controller for
controlling the functions of the A/D converter and the data
processor and the heating power supplied to the catheter, and (d) a
display unit coupled to the guidance device for displaying guidance
information based on the display signals.
[0017] In embodiments of the present invention, the display unit
may be an integral part of the guidance device or an independent
unit.
[0018] In one exemplary embodiment of the present invention, the
catheter guidance system further includes a power supply unit for
supplying electrical power to the catheter through the cable.
[0019] In one preferred embodiment of the present invention, the
guidance device keeps the heating power of the heating element of
the catheter constant and calculates a temperature difference
between temperature measurements in the media at the respective
locations of the two temperature measuring elements of the catheter
as an indication of the location of the front tip of the catheter
relative to the blood vessel wall of the patient's cardiovascular
system.
[0020] In another preferred embodiment of the present invention,
the guidance device keeps the temperature difference between
temperature measurements in the media at the respective locations
of the two temperature measuring elements of the catheter constant
and measures the heating power of the heating element of the
catheter as an indication of the location of the front tip of the
catheter relative to the blood vessel wall of the patient's
cardiovascular system.
[0021] In a practical implementation of the present invention, the
guidance information displayed on the display unit is a traffic
light type display comprising: (a) a red light indicating that the
front tip of the catheter is pressing through the blood vessel wall
of the patient's cardiovascular system; (b) a yellow light
indicating that the front tip of the catheter is contacting the
blood vessel wall of the patient's cardiovascular system; and (c) a
green light indicating that the front tip of the catheter is in the
bloodstream in the blood vessel of the patient's cardiovascular
system.
[0022] Also embodied and broadly described, the present invention
provides a catheter guidance system for use in the bloodstream of a
patient's cardiovascular system. The system comprises (a) a
catheter having a body with a front tip and a rear end, a heating
element disposed adjacent to the front tip for heating a media
surrounding the front tip in a blood vessel of a patient's
cardiovascular system, and two or more temperature measuring
elements adjacent to the heating element for measuring temperatures
located between the front tip and the heating element, and located
between the rear end and the heating element respectively in the
media; (b) a data processor for processing temperature measurement
signals from the two or more temperature measuring elements and
generating display signals indicative of the location of the front
tip of the catheter relative to the blood vessel wall of the
patient's cardiovascular system; (c) a controller for controlling
the data processor and a heating power supplied to the catheter;
and (d) a display unit for displaying guidance information based on
the display signals.
[0023] In one embodiment of the present invention, the system may
further comprises a cable electrically and electronically coupling
the catheter and the guidance device for providing electrical power
to the catheter and transmitting electronic signals of the heating
power and the temperature measurements from the catheter to the
guidance device.
[0024] Further embodied and broadly described, the present
invention provides a method for guiding a catheter through a
bloodstream of a patient's cardiovascular system, wherein the
catheter has a rear end and a front tip with a heating element for
heating a media surrounding the front tip in a blood vessel of the
patient's cardiovascular system. In one embodiment, the method
comprises: (a) generating temperature measurement signals from the
catheter representing measured temperatures in the media at
locations of the catheter adjacent to the heating element, in the
front of the heating element between the front tip and the heating
element, and in the back of the heating element between the rear
end and the heating element respectively; (b) processing the
temperature measurement signals and generating display signals
indicative of a location of the front tip of the catheter relative
to a blood vessel wall of the patient's cardiovascular system; and
(c) displaying guidance information based on the display
signals.
[0025] In one embodiment, the method further comprises the step of
transmitting electronic signals of the temperature measurements to
a guidance device. In another embodiment, it comprises the steps of
(a) supplying electrical power to the catheter; and (b) controlling
the heating power supplied to the catheter.
[0026] In one preferred embodiment of the present invention, the
method further comprises the steps of: (a) keeping the heating
power of the heating element of the catheter constant; and (b)
calculating a temperature difference between the temperature
measurements in the media at the locations in the front of the
heating element and the back of the heating element respectively as
an indication of the location of the front tip of the catheter
relative to the blood vessel wall of the patient's cardiovascular
system.
[0027] In another preferred embodiment of the present invention,
the method further comprises (a) keeping the temperature difference
constant between the temperature measurements in the media at the
front of the heating element and the back of the heating element;
and (b) measuring the heating power of the heating element of the
catheter as an indication of the location of the front tip of the
catheter relative to the blood vessel wall of the patient's
cardiovascular system.
[0028] In a practical implementation of the present invention, the
step of displaying guidance information further comprises the steps
of (a) displaying a red light indicating that the front tip of the
catheter is pressing through the blood vessel wall of the patient's
cardiovascular system; (b) displaying a yellow light indicating
that the front tip of the catheter is contacting the blood vessel
wall of the patient's cardiovascular system; and (c) displaying a
green light indicating that the front tip of the catheter is in the
bloodstream in the blood vessel of the patient's cardiovascular
system.
[0029] The catheter guidance system and method of the present
invention can simplify a task of a cardiologist, allow other
associate personnel who may not be necessarily as experienced as a
highly trained specialist to perform the medical procedures in the
bloodstream of a patient's cardiovascular system, and prevent
potentially dangerous perforation of blood vessels, especially when
blood vessel walls are brittle because of severe calcification. In
addition, the catheter guidance system and method of the present
invention are much safer than some conventional techniques such
X-ray because there will be no exposure to ionizing radiation.
Furthermore, the catheter guidance system of the present invention
is simple and low cost comparing to conventional equipment for
other techniques such as X-ray and ultrasound.
[0030] Additional features and advantages of the invention will be
set forth in the descriptions that follow and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure and steps
particularly pointed out in the written description and claims
thereof as well as the appended drawings.
[0031] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic block diagram illustrating an
exemplary catheter guidance system according to one embodiment of
the present invention.
[0033] FIG. 2a is a schematic sectional diagram illustrating an
exemplary situation where the catheter according to one embodiment
of the present invention is pressing through a blood vessel wall of
a patient's cardiovascular system.
[0034] FIG. 2b is a schematic diagram illustrating an exemplary
display corresponding to the situation shown in FIG. 2a.
[0035] FIG. 3a is a schematic sectional diagram illustrating
another exemplary situation where the catheter according to one
embodiment of the present invention is contacting a blood vessel
wall of a patient's cardiovascular system.
[0036] FIG. 3b is a schematic diagram illustrating an exemplary
display corresponding to the situation shown in FIG. 3a.
[0037] FIG. 4a is a schematic sectional diagram illustrating
another exemplary situation where the catheter according to one
embodiment of the present invention is in the bloodstream in a
blood vessel of a patient's cardiovascular system.
[0038] FIG. 4b is a schematic diagram illustrating an exemplary
display corresponding to the situation shown in FIG. 4a.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0039] Embodiments of the present invention provide a catheter
guidance system for medical procedures such as diagnostic
procedures and interventional procedures, such as but not limited
to radio-frequency (RF) ablation surgeries.
[0040] Referring to FIG. 1, it shows an exemplary catheter guidance
system 10 according to one embodiment of the present invention. The
catheter guidance system 10 includes a cardiac catheter 12 and a
guidance device 14, coupled by a cable 16. Catheter 12 has an
elongated body 20 with a front tip 22 and a rear end 24. Catheter
12 also has an internal chamber 26 that houses the internal
functional components of catheter 12. For clarity purposes, only
the components that relate to the design purpose and functions of
the present invention are shown.
[0041] In one embodiment of the present invention, the catheter 12
of FIG. 1 has a small heating element 30 and two temperature
measuring elements such as thermistors or thermocouples 32 and 34
located next to the heating element 30, with one temperature
measuring element 32 in front of the heating element 30 and the
other temperature measuring element 34 behind the heating element
30. The small heating element 30 and the two temperature measuring
elements 32 and 34 are placed inside the chamber 26 and in close
proximity of tip 22 of catheter 12. In one embodiment, they are
placed on the inner surface of the chamber 26. The small heating
element 30 heats tip 22 of catheter 12 to slightly higher than the
body temperature, and the temperatures measured by the temperature
measuring elements 32 and 34 provide information on the distance
between the catheter tip 22 and the blood vessel wall. In one
embodiment, the small heating element 30 heats tip 22 of catheter
12 to about 2-4 degrees above the body temperature.
[0042] It is understood that the heating element 30 and/or the two
temperature measuring elements 32 and 34 are not necessarily
located within a chamber of the catheter 12, but instead may be on
the outside surface of the catheter 12, or otherwise exposed to and
directly contacting the surrounding media (blood or tissue of the
blood vessel wall) in a blood vessel of a patient's cardiovascular
system. It is also understood that the number of temperature
measuring elements may not be limited to two, and multiple
temperature measuring elements may be used at different locations
near the heating element.
[0043] The catheter 12 may be maneuvered in a patient's
cardiovascular system either upstream (against the direction of the
blood flow) or downstream (along the direction of the blood flow).
By providing at least two temperature measuring elements 32 and 34
at the opposite sides of the heating element 30, the device of the
embodiments of the present invention allows a measurement of
temperature changes in both situations.
[0044] When catheter 12 is traveling upstream (i.e., against the
direction of the blood flow), the blood surrounding the catheter 12
is flowing from the front tip 22 to the rear end 24 of the catheter
12. The media (blood or tissue of the blood vessel wall) first
contacts the front temperature measuring element 32 before it is
heated by the heating element 30, so the temperature measured by
the front temperature measuring element 32 is close to the normal
temperature of the media (e.g., the body temperature of the
patient) which may be used as a base temperature. As the media
contacts the heating element 30 is heated by the heating element
30, the heat is carried by the media towards the location of the
rear temperature measuring element 34. The temperature measured by
the temperature measuring element 34 will be higher than the base
temperature because the media is heated by the heating element 30.
If the thermal conductivity of the media is high (e.g., when the
media is blood), then the heat loss from the location of the
heating element 30 to the location of the rear temperature
measuring element 34 will be great, and the temperature difference
between the temperatures measured by the temperature measuring
elements 32 and 34 will be small. Particularly at the center of the
blood vessel and in the middle of the bloodstream, the velocity of
blood flow is highest so that the thermal conductivity is also
highest, which means that the heat loss from the location of the
heating element 30 to the location of the rear temperature
measuring element 34 is greatest, and the temperature difference
between the temperatures measured by the temperature measuring
elements 32 and 34 is smallest. On the other hand, if the thermal
conductivity of the media is low (e.g., when the media is blood
vessel wall), then the heat loss will be minimal from the location
of the heating element 30 to the location of the rear temperature
measuring element 34, and the temperature difference between the
temperatures measured by the temperature measuring elements 32 and
34 will be large. Therefore, the difference between the two
temperatures measured by the temperature measuring elements 32 and
34 can be used to indicate whether the catheter 12 is pressing
through, contacting, or away from the blood vessel wall. When
catheter 12 is traveling downstream (i.e., along the direction of
the blood flow), the blood surrounding the catheter 12 is flowing
from the rear end 24 to the front tip 22 of the catheter 12. The
media (blood or tissue of the blood vessel wall) first contacts the
rear temperature measuring element 34 before it is heated by the
heating element 30, so the temperature measured by the rear
temperature measuring element 34 is close to the normal temperature
of the media (e.g., the body temperature of the patient) which may
be used as a base temperature. As the media contacts the heating
element 30 is heated by the heating element 30, the heat is carried
by the media towards the location of the front temperature
measuring element 32. The temperature measured by the temperature
measuring element 32 will be higher than the base temperature
because the media is heated by the heating element 30. If the
thermal conductivity of the media is high (e.g., when the media is
blood), then the heat loss from the location of the heating element
30 to the location of the front temperature measuring element 32
will be great, and the temperature difference between the
temperatures measured by the temperature measuring elements 32 and
34 will be small. Particularly at the center of the blood vessel
and in the middle of the bloodstream, the velocity of blood flow is
highest so that the thermal conductivity is also highest, which
means that the heat loss from the location of the heating element
30 to the location of the front temperature measuring element 32 is
greatest, and the temperature difference between the temperatures
measured by the temperature measuring elements 32 and 34 is
smallest. On the other hand, if the thermal conductivity of the
media is low (e.g., when the media is blood vessel wall), then the
heat loss will be minimal from the location of the heating element
30 to the location of the front temperature measuring element 32,
and the temperature difference between the temperatures measured by
the temperature measuring elements 32 and 34 will be large. Again,
the difference between the two temperatures measured by the
temperature measuring elements 32 and 34 can be used to indicate
whether the catheter 12 is pressing through, contacting, or away
from the blood vessel wall.
[0045] Accordingly, the catheter design of the embodiments of the
present invention with at least two temperature measuring elements
32 and 34, one located in front of the heating element 30 and the
other located behind the heating element 30, enables the
embodiments of the present invention to handle both situations:
whether the catheter is maneuvered to travel upstream or downstream
in the blood vessel of a patient's cardiovascular system.
[0046] The small heating element 30 and temperature measuring
elements 32 and 34 are all coupled to the cable 16 which leads from
the end 24 of the catheter to the guidance device 14. Electrical
power to the healing element 30 may be provided by guidance device
14 through a wiring element of cable 16. In addition, the
electronic signals from the temperature measuring elements 32 and
34 and heating element 30 are transmitted to the guidance device 14
through the same or additional wiring element of cable 16.
[0047] The signals from the temperature measuring elements 32 and
34 are received, analyzed and processed by the guidance device 14.
The guidance device 14 may include an analog/digital (A/D)
converter 42 for converting the analog temperature measurement
signals to digital signals, which are then processed by a data
processor 44. Alternatively, the analog signals may be processed
directly by the data processor. The guidance device also includes a
control circuit 46 for control the functions of the A/D converter
42 and data processor 44, and may also control the heating power of
the heating element 30 of the catheter 12. The guidance device may
further includes a power converter/supply unit (not shown) that
converts alternate current (AC) power to direct current (DC) power
and supply electrical power to the catheter 12.
[0048] The analog data of heating power may also be transmitted to
the A/D converter 42 for further processing and analysis by the
data processor 44. There are a number of options on how the
guidance device 14 controls the heating element 30 and collects and
analyzes the temperature measurement of the temperature measuring
element 32 and 34. Therefore there are a number of different
algorithms that may be applied to process the data.
[0049] For example, the guidance device may keep the heating power
of the heating element 30 constant, and calculate the temperature
difference in the media between the respective locations of the two
temperature measuring elements 32 and 34. The data processor then
applies an algorithm wherein the temperature difference between
temperature measuring elements 32 and 34 is reversely proportional
to the heat loss in the media near the tip 22 of the catheter 12.
As discussed earlier, in this scenario a large temperature
difference will indicate that the media is blood vessel wall, while
a small temperature difference will indicate that the media is
blood, and an even smaller temperature difference will indicate
that the catheter tip 22 is further away from the blood vessel
wall, i.e., safely located near the middle or center of the blood
vessel of the patient's cardiovascular system.
[0050] Alternatively the guidance device may keep the temperature
difference in the media between the respective locations of the two
temperature measuring elements 32 and 34 constant, and measure the
heating power of the heating element 30. The data processor then
applies an alternative algorithm wherein the heating power of the
heating element 30 is proportional to the heat loss in the media
near the tip 22 of the catheter 12. As discussed earlier, blood has
a higher heat loss than blood vessel wall, and the blood flow in
the middle of blood vessel has the highest heat loss. Therefore, in
this alternative scenario a low heating power (proportional to low
heat loss) will indicate that the media is blood vessel wall, while
a higher heating power (proportional to high heat loss) will
indicate that the media is blood, and an even higher heating power
(proportional to even higher heat loss) will indicate that the
catheter tip 22 is further away from the blood vessel wall, i.e.,
safely located near the middle or center of the blood vessel of the
patient's cardiovascular system.
[0051] After the signals are analyzed, the data processor 44 will
generate and send display signals to a display 48 for visually
displaying guidance information indicative of the location of the
catheter tip 22 relative to the blood vessel wall as an aid to an
interventional cardiologist performing RF ablation. The information
displayed may be represented by, for example, a traffic light type
of display to provide an easy and intuitive guidance.
[0052] Referring to FIGS. 2a and 2b, when the signals processed by
the data processor 44 indicate that the catheter is pressing
through the blood vessel wall as shown in FIG. 2a, the display 48
may display a red light to indicate that the catheter tip 22 is
pressing through the wall of a blood vessel. The red light provides
a visual warning of a high perforation risk.
[0053] Referring to FIGS. 3a and 3b, when the signals processed by
the data processor indicate that the catheter is contacting the
blood vessel wall as shown in FIG. 3a, the display 48 may display a
yellow light to indicate that the catheter tip 22 is contacting the
wall of a blood vessel. The yellow light provides a visual warning
of a potential perforation risk.
[0054] Referring to FIGS. 4a and 4b, when the signals processed by
the data processor indicate that the catheter is in the middle of a
blood vessel away from the blood vessel wall as shown in FIG. 4a,
the display 48 may display a green light to indicate that the
catheter tip 22 is safely away from the wall of a blood vessel. The
green light provides a visual indication of safe maneuvering of the
catheter 12.
[0055] It is noted that other types of display may be utilized to
provide a visual and intuitive guidance to an interventional
cardiologist performing a medical procedure. It is also noted that
the display 48 may be an integral part of the guidance device 14,
or a separate display unit coupled to the guidance device 14. It is
further noted that the guidance device 14 may be incorporated into
and become a part of an existing RF ablation or catheter controller
device.
[0056] The catheter guidance system and method of the embodiments
of the present invention have many advantages. They provide a novel
way to monitor the distance between the tip of an RF ablation
catheter and the blood vessel wall for safely navigating the
catheter in the bloodstream. They also provide an intuitive visual
indication to an interventional cardiologist that helps him or her
to avoid potentially dangerous perforation of blood vessels,
especially when blood vessel walls are brittle because of severe
calcification. They simplify a task of an interventional
cardiologist and might allow associate personnel with less
experience to perform such procedures. They also improve the
success rate of a RF ablation procedure which highly depends on the
contact area between the catheter tip and the blood vessel wall.
They further increase the safety of medical procedures involving
catheters by avoiding exposure to ionizing radiation associated
with X-ray, and also reduces the costs of such procedures as
compared to X-ray and ultrasound. Moreover, the guidance system and
method of the embodiments of the present invention can also be used
in other applications such as endoscopy, urology, gynecology and
pulmonology.
[0057] It will be apparent to those skilled in the art that various
modification and variations can be made to the system and method of
the present invention without departing from the spirit or scope of
the invention. Thus, it is intended that the present invention
cover modifications and variations that come within the scope of
the appended claims and their equivalents.
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